The invention involves an unbalanced vibrator for compacting concrete components during their manufacture, in particular an unbalanced vibrator having a vibrating table, unbalance shafts arranged on the vibrating table, and electronic motors allocated to the unbalance shafts for driving them, wherein the unbalanced vibrator has a device for the control and/or regulation of the rotational speed and/or the relative phase position of the unbalance shafts.
A device of this type is known, for example, from German utility model DE-U-297 12 242. According to this document, asynchronous three phase a.c. motors are used as electronic motors, and the unbalance shaft control or regulation is accomplished via vector regulators.
It is disadvantageous in this known device that asynchronous machines react relatively sluggishly to the corresponding control or regulation signals. Since, however, even a slight angular displacement of the unbalance shafts in their "neutral position" can lead to an undesired vibration of the vibrating table, this is considered a disadvantage.
Also, from German published patent application DE-A-43 17 351, a comparable vibrating device is known. According to this document, incremental transmitters are provided in order to detect the position that the unbalanced masses have relative to each other. However, these incremental transmitters have a very limited resolution so that the system also has only limited synchronization properties.
In a vibrating device, as is known from German published patent application DE-A-44 07 013, operation is by hydraulic actuators and servo components. These are relatively sluggish, and thus this system is likewise limited in its dynamics. Since the adjustment times are longer, the cycle times are also prolonged, for example, during block manufacturing. Also, the transmitters used in the prior art in order to detect the position of the unbalance shafts are incremental transmitters having only a limited resolution, which has an unfavorable effect, just as the poor dynamics, on the control performance of the device.